Fibers water vapor adsorption

Figure 3 shows the water-vapor adsorption isotherms measured on the silane-treated fibers along with those obtained on the untreated fibers. A complete discussion of the water adsorption isotherms of the untreated fibers has already been reported [8]. Here, two new features are immediately evident. First, the presence of the silane overlayer has greatly enhanced the water adsorption capacity of the fibers, and, second, the silane-treated fibers that contain 4% and 6% B,0, adsorb significantly more water than the 0% B20, fibers. It is important to note that these data have been normalized to the specific surface areas of the... 

Figure 3. Water-vapor adsorption isotherms for glass fibers after the silane treatment the isotherms for the untreated fibers with 0% and 6% B,0, are included. APS - 1% solution of y-aminopropyl-silane at pH 10 0%—O,4% Oand6% B.

The primary effect of B,0, in the silane-treated glass fibers was found to be an enhancement of the water adsorptivity. This dependence on B203 was also observed in the water adsorption behavior of untreated fibers, water-vapor hydrated fibers, and water-leached fibers [8], but was significantly greater after the silane treatment. It was also found that the presence of B,03 influenced the amount of silane adsorption per se. Altogether it can be concluded that there is a direct effect of B,0, on water adsorption. There is also an influence of B,03 on the adsorption and condensation of aminosilane which determines the water adsorptivity of the silane-treated fiber. 

There have been several applications of IGC to the determination of sur ce interactions (15-24). In particular, IGC was applied to several studies of natural polymers. Among them are cellulose (2, wood (26), potato starch as Amylopectin (27) and lignocellosic surfaces (2S). In these studies, die surface diermodynamic characteristic of wood fiber and its relationship to the fiber s water vapor adsorption was determined by IGC (26) Also, the surface ener, surface acid-base flee energy, enthalpy of desorption of acid-base probes, surface acid-base acceptors, and donor parameters were determined by IGC (26). Cellulose was also found by IGC to be sensitive to the presence of adsorbed water which possibly disorders its surface structure. 

Evolution of the external surface area and the two types of microporosity of atiapulgite (structural and inter-fiber) were examined as a function of a vacuum thermal treatment upt to 500°C. The methods used include controlled transformation rate thermal analysis, N2 and Ar low temperature adsorption calorimetry, water vapor adsorption gravimetry and quasi equilibrium gas adsorption procedure of N2 at 77K and CO2 at 273 and 293K. Depending on the outgassing conditions,i.e. the residual pressure, the structure folds 150 to 70 C. For lower temperature, only a part (18%) of the structural microp< osity is available to N2,13% to argon and 100% to CC>2.With water, the structure can rehydrate after the structure is folded up to an outgassing temperature of 225°C. 

Denoyel et al. [45] derived the pore size distributions of two sets of activated carbons (one activated in water vapor and the other activated with phosphoric acid) using immersion calorimetric data. They concluded that immersion calorimetry is a convenient technique to assess the total surface area available for a given molecule and the micropore size distribution. More recently, Villar-Rodil et al. [46] have followed this approach to characterize the porous texture of a series of NomexO-derived carbon fibers activated to various bum-offs using liquids with different molecular dimensions as well as N2 and CO2 adsorption Isotherms. Table 3 includes the immersion enthalpies and corresponding surface areas. Relative changes in surface area accessible to the different adsorbates were ascribed to... 

Owing to the method of contact-angle or surface-energy measurement, the surface of wool necessarily includes the region between cuticle cells in addition to the cuticle itself Horr has further suggested that vapor adsorption due to capillary condensation may occur at the fiber cuticle scale edges, and that the phenomenon may contribute to the above interpretation that the wool surface is not entirely methyl. Horr also found that the possible composition of the wool fiber surface may even vary depending on the liquid with which it is in contact (e.g., water or methylene iodide). 

Smoothed Values of Dry-Basis Moisture Content (kg/kg) for the Adsorption of Water Vapor at 30°C onto Fibers... 

The fractal approach was also used to investigate adsorption and desorption mechanisms of water vapor on active carbons that were derived from coconut shell, coal, coke and pitch fiber featuring a wide range of BET specific surface areas [78]. A values were measured for the water clusters adsorbed on primary carbon centers. Values ranging from 1.64 to 1.67 implied a diffusion-limited aggregation model on a pore wall plane, whereas higher A values (up to 1.86), measured at a relative pressure X = 0.95, implied the formation of water clusters that were partly merged vertically to the walls. 

A. Pore size distribution determined from adsorption isotherm of water vapor on collagen fiber... 

A. Pore Size Distribution Determined from Adsorption Isotherm of Water Vapor on Collagen Fiber... 

The pore size distribution of collagen fiber is determined by using adsorption isotherms of water vapor or nitrogen gas. The preparation of the sample, adsorption procedure, and calculation method are mentioned below. 

The pore size distribution is ealculated based on the water vapor or nitrogen gas adsorption isotherm. Before the calculation, it is essential to obtain an accurate adsorption isotherm. The amount of nitrogen gas adsorbed on the collagen fiber is extremely low in comparison to the amount of water vapor adsorbed on it. Approximately. 1 x 10 kg of collagen fiber, therefore, is put in the adsorption glass bulb. The amount adsorbed on the collagen fiber is measured at equilibrium pressures of 6.7, 13.3, 20.0, 26.7, 33.3, 40.0, 53.3, 66.7, 80.0, 93.3, and 101.3 kPa in order to get an accurate quantity. The adsorption isotherm for each... 

Adsorption and migration of the water vapor along the fiber surface ... 

TABLE 1 Smoothed values of dry-basis moisture content (kg/kg) for the adsorption of water vapor at 30°C onto textile fibers. 

The second stage features the moisture sorption of fibers, which is relatively slow and takes a few minutes to a few hours to complete. In this period, water sorption into the fibers takes place as the water vapor diffuses into the fabric, which increases the relative humidity at the surfaces of fibers. After liquid water dififiises into the fabric, the surfaces of the fibers are saturated due to the film of water on them, which again will enhance the sorption process. During these two transient stages, heat transfer is coupled with the four different forms of liquid transfer due to the heat released or absorbed during sorption/adsorption and evaporation/conden-sation. Sorption/ adsorption and evaporation/condensation, in turn, are affected by the efficiency of the heat transfer. For instance, sorption and evaporation in thick cotton fabric take a longer time to reach steady states than in tiiin cotton fabrics. 

Sorption equilibria and kinetics are influenced by the nature of the adsorbent and the adsorbate, by the mechanism of adsorption, and by environmental parameters such as temperature, relative humidity, concentration of the adsorbate, and air velocity and turbulence past the adsorbent surface. Air velocity and turbulence only affect sorption kinetics the other parameters also affect equilibria. In general, low adsorbate saturation vapor pressure, low temperature, and high adsorbate concentration in the air increase adsorption. Relative humidity does not always affect adsorption. Colombo et al. (1993) found a 35 % decrease in adsorbed mass when relative humidity was changed from <10 % to 35 %, but only an 8 % decrease when the humidity was increased from 35 % to 70 %. Building materials, which are exposed to indoor air in the normal humidity range of 35-70 %, will typically already be covered by at least one monolayer of adsorbed water, and the formation of multilayers will only have a limited influence on sorption properties for other airborne substances. Kirchner et al. (1997) found that an increase in air velocity increased the rate of desorption of a VOC mixture from painted gypsum, but not from carpet. The air velocity of air above the tuft may be insignificant for the desorption processes of carpet fibers deeper in the tuft. 

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